全文获取类型
收费全文 | 199990篇 |
免费 | 7873篇 |
国内免费 | 3946篇 |
专业分类
化学 | 113162篇 |
晶体学 | 2782篇 |
力学 | 9348篇 |
综合类 | 143篇 |
数学 | 20649篇 |
物理学 | 65725篇 |
出版年
2022年 | 1952篇 |
2021年 | 2185篇 |
2020年 | 2470篇 |
2019年 | 2457篇 |
2018年 | 2273篇 |
2017年 | 2153篇 |
2016年 | 3859篇 |
2015年 | 3323篇 |
2014年 | 4319篇 |
2013年 | 9956篇 |
2012年 | 9000篇 |
2011年 | 10699篇 |
2010年 | 6680篇 |
2009年 | 6763篇 |
2008年 | 9232篇 |
2007年 | 8943篇 |
2006年 | 8573篇 |
2005年 | 7737篇 |
2004年 | 6780篇 |
2003年 | 5779篇 |
2002年 | 5687篇 |
2001年 | 6570篇 |
2000年 | 5000篇 |
1999年 | 4052篇 |
1998年 | 3121篇 |
1997年 | 3098篇 |
1996年 | 3051篇 |
1995年 | 2696篇 |
1994年 | 2495篇 |
1993年 | 2301篇 |
1992年 | 2615篇 |
1991年 | 2527篇 |
1990年 | 2219篇 |
1989年 | 2148篇 |
1988年 | 2119篇 |
1987年 | 2037篇 |
1986年 | 1971篇 |
1985年 | 2847篇 |
1984年 | 2785篇 |
1983年 | 2250篇 |
1982年 | 2419篇 |
1981年 | 2294篇 |
1980年 | 2233篇 |
1979年 | 2175篇 |
1978年 | 2243篇 |
1977年 | 2199篇 |
1976年 | 2130篇 |
1975年 | 2119篇 |
1974年 | 2023篇 |
1973年 | 2105篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Immobilized Catalysts for Iridium‐Catalyzed Allylic Amination: Rate Enhancement by Immobilization 下载免费PDF全文
Dr. Chandi C. Malakar Prof. Dr. Günter Helmchen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(19):7127-7134
The first immobilized catalyst for Ir‐catalyzed asymmetric allylic aminations is described. The catalyst is a cationic (π‐allyl)Ir complex bound by cation exchange to an anionic silica gel support. Preparation of the catalyst is facile, and the supported catalyst displayed considerably enhanced activity compared with the parent homogeneous catalyst. Up to 43 consecutive amination runs were possible in recycling experiments. 相似文献
92.
93.
94.
L. Resse L.G.S. Oliveira C.I.L. de Araujo A.R. Pereira R.L. Silva 《Physics letters. A》2019,383(14):1655-1659
In this work, we have used the MuMax3 software to simulate devices consisting of a ferromagnetic thin film placed over a heavy metal thin film. The devices are two interconnected partial-disks where a Néel domain wall is formed in the disks junction. In our simulations we investigate devices with disk radius nm and different distance d between the disks centers (from nm to nm). By applying strong sinusoidal external magnetic fields, we find a mechanism able to create, annihilate and even manipulate a skyrmion in each side of the device. This mechanism is discussed in terms of interactions between skyrmion and domain wall. The Néel domain wall formed in the center of the device interacts with the Néel skyrmion, leading to a process of transporting a skyrmion from one disk to the other periodically. Our results have relevance for potential applications in spintronics such as logical devices. 相似文献
95.
96.
Yu Wang Xin-jing Zhao Rong-Jing Wei Gui-jie Liang Kang Wang Yuan-zhi Tan Ye Yang 《化学物理学报(中文版)》2021,34(5):591-597
The intermolecular interaction determines the photophysical properties of the organic aggregates, which are critical to the performance of organic photovoltaics. Here, excitonic coupling, an important intermolecular interaction in organic aggregates, between the π-stacking graphene quantum dots is studied by using transient absorption spectroscopy. We find that the spectral evolution of the ground state bleach arises from the dynamic variation of the excitonic coupling in the excited π-stacks. According to the spectral simulations, we demonstrate that the kinetics of the vibronic peak can be exploited as a probe to measure the dynamics of excitonic coupling in the excited π-stacks. 相似文献
97.
Probing the Catalytic Activity of Reduced Graphene Oxide Decorated with Au Nanoparticles Triggered by Visible Light 下载免费PDF全文
Dr. Jiale Wang Dr. Fabiane J. Trindade Caroline B. de Aquino Joana C. Pieretti Prof. Dr. Sergio H. Domingues Prof. Dr. Romulo A. Ando Prof. Dr. Pedro H. C. Camargo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(27):9889-9894
Hybrid materials in which reduced graphene oxide (rGO) is decorated with Au nanoparticles (rGO–Au NPs) were obtained by the in situ reduction of GO and AuCl4?(aq) by ascorbic acid. On laser excitation, rGO could be oxidized as a result of the surface plasmon resonance (SPR) excitation in the Au NPs, which generates activated O2 through the transfer of SPR‐excited hot electrons to O2 molecules adsorbed from air. The SPR‐mediated catalytic oxidation of p‐aminothiophenol (PATP) to p,p′‐dimercaptoazobenzene (DMAB) was then employed as a model reaction to probe the effect of rGO as a support for Au NPs on their SPR‐mediated catalytic activities. The increased conversion of PATP to DMAB relative to individual Au NPs indicated that charge‐transfer processes from rGO to Au took place and contributed to improved SPR‐mediated activity. Since the transfer of electrons from Au to adsorbed O2 molecules is the crucial step for PATP oxidation, in addition to the SPR‐excited hot electrons of Au NPs, the transfer of electrons from rGO to Au contributed to increasing the electron density of Au above the Fermi level and thus the Au‐to‐O2 charge‐transfer process. 相似文献
98.
Highly Selective Copper‐Catalyzed Asymmetric [3+2] Cycloaddition of Azomethine Ylides with Acyclic 1,3‐Dienes 下载免费PDF全文
María González‐Esguevillas Ana Pascual‐Escudero Dr. Javier Adrio Prof. Dr. Juan C. Carretero 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(12):4561-4565
The first examples of the catalytic asymmetric 1,3‐dipolar cycloaddition of azomethine ylides with acyclic activated 1,3‐dienes (and 1,3‐enynes) are described. Under copper catalysis, a selective cycloaddition at the terminal γ,δ‐C?C bond is observed. In addition, depending on the ligand used, either the exo or the endo adduct can be obtained with high selectivity. Under appropriate reaction conditions, the acyclic 1,6‐addition product is detected, suggesting a stepwise mechanism. The resulting C4‐alkenyl‐substituted pyrrolidines are suitable substrates for further access to polycyclic systems, as highlighted by the preparation of hexahydrochromeno[4,3‐b]pyrrole and the tetracyclic core of the alkaloid gracilamine. 相似文献
99.
100.
Abstract Gastrodigenin, also known as 4-hydroxybenzyl alcohol (HBA), is one of the main components of Gastrodia elata, which is a perfect lead compound of natural products. In order to get new active compounds, we modified the structure of HBA through esterification with carboxylic acid, and got a series of derivatives in which 4-hydroxybenzyl alcohol 2-naphthoate (NHBA) showed stronger antidepressant activity than HBA. In this paper, we firstly evaluated the antidepressant activity of NHBA by tail suspension test (TST) and forced swimming test (FST). Then, we carried out the biochemical assay and western blot to determine its mechanism. The results displayed that NHBA could increase the content of serotonin, dopamine, norepinephrine, γ-aminobutyric acid, brain-derived neurotrophic factor (BDNF) and tropomyosin receptor kinase B (TrkB) in mice brain. It suggested that NHBA exhibited an antidepressant-like effect through monoaminergic system, GABAergic system and BDNF/TrkB signaling pathways. 相似文献